Abstract

Maanshan Nuclear Power Station is a two-unit Westinghouse three-loop PWR power station. This research studies the simulation of Maanshan SBO accident happened on 18th March, 2001, and thermal-hydraulic phenomena of the plant during station blackout with and without mitigation strategies. The modeling and simulation works were done by using TRACE code, which is a best-estimate thermal-hydraulic system code developed by US NRC. The purpose of using the mitigation strategy during SBO is to cool down NSSS as soon as possible, to keep the fuel covered by water, and not to let peak cladding temperature (PCT) higher than 1088K (1500°F), which is the temperature that metal-water reaction can self-sustain. Actions that considered such as operation of auxiliary feedwater system, depressurization of steam generators (SG), and line-up the alternate water sources such as sea water when regular systems aren't available.

The simulations of mitigation strategies start from normal operation at 100% power then an earthquake is assumed to happen, tsunami strike the site 20 minutes later, and failure of turbine driven auxiliary feedwater is assumed in base cases. Two different basic mitigation strategies were simulated, include (1) SG controlled-depressurization at the time that SBO happen and SG alternate injection after 1 hour of SBO, (2) SG depressurization at the time after 1 hour of SBO that injection is ready. In addition, alternate injection preparation time is further extended to find the longest acceptable value. Reactor coolant pump shaft seal leakage is also considered in all cases.